**dBm (Decibel-milliwatts)** is a unit of power relative to 1 milliwatt. **dB (Decibels)** is a unit of ratio that expresses the relationship between two values of power, voltage, or intensity. It’s also logarithmic.

To convert a dBm value to dB, you need to specify a reference value.

In the calculator, enter dBm value dbm1 and reference value dBm2. The tool will calculate the ratio in dB

## Formula

**dB = dBm _{1} – dBm_{2}**

**Example**

If

**dBm**_{1}= 40 dBm**dBm**_{2}= 30 dBm

then,

**dBm _{1} – dBm_{2} = 10 dB**

Note that this is not the difference in power level between the two. For that use this calculator.

Instead it is the ratio of powers which has no units.

- dBm1 = 40 dBm = 10 Watt
- dBm2 = 30 dBm = 1 Watt

The ratio between the two is 10 and on the log scale it works out to:

**10*Log _{10}(10) = 10 dB**

**Other Conversions**

This calculator lets you convert between Volt and dBm.

dB is a relative number and represents a ratio between two quantities. In communications engineering, dB is used to represent the signal-to-noise ratio, gain of an amplifier and more.

**Try our other calculators**